Technical Abstract:
Agricultural plant wastes, when properly processed into useful commodities, can become an economic asset for the particular crop. The extraction of latex rubber from the guayule plant (Parthenium argentatum Gray) will involve about 10% of the harvested material. Uses must be found for the remaining 90% plant residue, or bagasse. One application is to process the bagasse into renewable, compact pellet-type fuel that can be used at the site or transported to the consumer, whichever will prove the most profitable. Furnace and water heaters that can burn pelletized plant materials have become popular and their safety, low pollution, and reasonable operational costs have been demonstrated. Also, the drastic increases in the price of liquified fuel and its uncertain supply place a premium for finding and using alternate, low-cost, cellulose-based fuels.
The objectives of our study were to fabricate pellet fuel from guayule bagasse and to determine its physical properties and burning characteristics.
Guayule bagasse remaining from the latex extraction process and byproducts from a local cotton gin were collected and air-drid in a greenhouse to approximately 6% water content. A blend of 75% guayule bagasse and 25% processed cotton gin byproducts were mixed and pelleted to a density of 534 kg/m3 (33.34 lb/ft3).
Stable pellets (6mm diameter x 25 mm long)were produced with a commercial pellet mill that did not require additional ginding agents. The processed cotton gin material provided the lubricant and some of the binding agent. The resinous material that was still in the guayule bagasse also contributed to the binding. The energy equivalent was about 22.49 Mj/kg (9670 BTU/lb) and approximately 10% higher than presently available pellet fuels. The guayule resin is reported to have an energy value of about 38.0 Mj/kg (16,400 BTU/lb), and because it makes about 10% of the bagasse material, this fraction contributed to the energy value of the pellet. The ash content was about 5.0% and the sodium oxide 4.6%. The sodium ash was high because sodium sulfite is included in the latex extraction solution as an antioxidant. This sodium fraction could be readily removed by washing the bagasse after the last step in the latex extraction procedure. The pellets were fed and burned easily in a commercially available pellet stove. The average combustion efficiency of the guayule/gin byproduct pellets was 90.9%, comparing favorably with the 96.8% obtained from burning premium-grade wood pellets.
A blend of guayule bagasse with cotton gin byproducts provided the raw materials needed to make pellet fuel that has economic potential. These waste materials can be considered as useful and renewable bioenergy sources.